<!-- <nz-dropdown [nzPlacement]="'bottomLeft'" [nzTrigger]="'click'">
    <button nz-button nz-dropdown>Add Online Map</button>
    <ul nz-menu>
      <li nz-menu-item *ngFor="let layer of onlineLayers" (click)="addOnlineLayer(layer)">
        {{layer.name}}
      </li>
    </ul>
  </nz-dropdown> -->